SD Card

Discussion in 'Canon Accessories' started by erikpottas, Mar 14, 2019 at 2:02 PM.

  1. erikpottas

    erikpottas TPF Noob!

    Feb 9, 2019
    Likes Received:
    Today I downloaded a few photo and when I was done I just pulled it out but the SD Card folder was still open and was still downloading onto my computer. So is my SD Card fine or should I not insert it into my camera anymore?

    Sent from my EML-L09 using Tapatalk

  2. zombiesniper

    zombiesniper Furtographer Extraordinaire! Supporting Member

    Jun 23, 2015
    Likes Received:
    Angus, Ontario
    Can others edit my Photos:
    Photos NOT OK to edit
    Did you get all of the files off?
    If no. Put it back in and download the files. Then format it and it'll be fine to go back in the camera.
    Done it a few times.
  3. TCampbell

    TCampbell Been spending a lot of time on here!

    Mar 31, 2012
    Likes Received:
    Dearborn, MI
    Can others edit my Photos:
    Photos OK to edit

    The main problem with pulling a card without properly telling the computer to "eject" the card has to do with activity in which the computer is writing to the card (not so much when reading).

    Computer storage is allocated in "blocks". Block-sizes vary based on the specific storage device, but a "block" is the smallest unit of space that a computer can read or write to a storage device. If the computer just wants to write one single character to a file, it has to write an entire block to do it. If it is editing a file, it has to "read" the block (so it has an in-memory copy), then it has to modify that one character, then it has to "write" that modified block back to the storage device ... all to just change one character.

    On a typical memory card of either 16GB or 32GB size, the card is probably formatted as a FAT32 filesystem. The block size for FAT32 between 16-32GB is 16KB. This means that in order to change just one single character (one byte) you have to re-write 16,384 characters (the one you want to change, and 16,383 characters that you didn't want to change but have to be re-written anyway). You can see how that isn't very efficient and depending on the application, saving to files could be extremely inefficient. Don't worry... there's a strategy to deal with this.

    The strategy is "buffered" writing. When a computer needs to write something to a file, it really just "writes" to a memory buffer (this is space in the computer's memory and not space on the storage device). When the buffer has enough data to justify writing a "block" the storage device, it performs the actual "write" and clears the buffer (so now the buffer is ready to accumulate more data that will eventually also get saved to the storage device).

    If you pull a memory card and there was buffered data that had not yet been saved to the card, that information will be lost (and a file could be corrupted depending on what the computer was doing with the file.)

    When you "eject" a storage device, the computer will make sure that (a) no applications are currently using the device, and (b) all un-saved (buffered data) is saved to the card (sometimes called "flushing" the buffer) and the computer will tell you when it is ok to remove the card (after the final buffered blocks are written.)

    As you were "reading" from the card, you wouldn't have any buffered data that needed to be written to the card (you were writing... you were reading). So your memory card is almost certainly fine.

    BUT... you should get in the habit of "ejecting" storage devices before you pull them.

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